Depends on what year B-body housing you have. There are Five different versions, all different widths and spring perch location...
B BODY
'62-'63= 53 1/4" (And '64 Max Wedge)
'64 = 55 5/8" (Exc. Max Wedge)
'65-'67= 54 1/4"
'68-'70= 54 15/16"
'71-'74= 57 7/8"
'71-'73 wagon= 59 7/16"
This should be easy to figure out once you identify which one you have.
I run a FACTORY 8 3/4" rear housing, and I fit a 15x8 rim, with 4.5" backspace, with 255 60r15 tire, Perfectly on the back of my 72 dart.
"Googling" '8 3/4 rear end dimensions' tells us that;
Factory A-body flange to flange is 52 5/8"...
...so just figure out the difference in width flange to flange, divide it by two, and you will have how much longer the housing 'sticks out' from the factory A-body location...
For example.
If we go with the 65-67 B-body housing, the difference in overall flange to flange length is 1 5/8". Divide that by 2, and you get 13/16". That is how much more the tube will stick out past factory A-body housing location.
So you need a wheel that is roughly 13/16" more backspace than the baseline. I used 15x8 with 4.5" BS as my baseline since I know that fits centered in the wheel housing.
May sound confusing but play around with it on paper and it works out well. I'd run a 5"-5.5" backspace wheel and that will get you close to center, depending on how wide you order the wheel.
